Key Caveats to Prescribing Fosfomycin for UTI Treatment
Fosfomycin is recommended only for uncomplicated cystitis in women and should not be used for pyelonephritis, complicated UTIs, or in men due to limited efficacy data for these conditions. 1, 2, 3
Indication Limitations
- Fosfomycin is FDA-approved only for uncomplicated urinary tract infections (acute cystitis) in women due to susceptible strains of Escherichia coli and Enterococcus faecalis 3
- Not indicated for pyelonephritis, perinephric abscess, or complicated UTIs 2, 3
- Not recommended for routine use in men with UTIs, as clinical efficacy data is limited in this population 1
Dosing Considerations
- Only a single 3-gram oral dose should be used to treat a single episode of acute cystitis; repeated daily doses did not improve outcomes but increased adverse events 3
- For ESBL-producing organisms causing uncomplicated cystitis, the same single 3-gram dose is recommended 4
- Off-label multiple-dose regimens (every 48-72 hours for 3 doses) have been used for complicated UTIs, but this is not FDA-approved 5
Efficacy Concerns
- Bacterial efficacy is somewhat lower than other first-line agents, though clinical efficacy is comparable 2
- If symptoms persist or recur within 2 weeks after treatment, urine culture and susceptibility testing should be performed 1, 3
- If bacteriuria persists or reappears after treatment, alternative agents should be selected 3
Drug Interactions
- Metoclopramide and other drugs that increase gastrointestinal motility lower serum concentration and urinary excretion of fosfomycin 3
- Cimetidine does not affect fosfomycin pharmacokinetics when co-administered 3
Adverse Effects
- Common adverse effects include diarrhea, nausea, and vomiting 2, 3
- Patients should be informed about the possibility of developing antibiotic-associated diarrhea, including C. difficile-associated diarrhea 3
Special Populations
- In pregnancy, fosfomycin crosses the placental barrier; use only if clearly needed 3
- For pregnant women with asymptomatic bacteriuria, standard short-course treatment or single-dose fosfomycin is recommended 1
- Not recommended for asymptomatic bacteriuria except in pregnant women and before urological procedures breaching the mucosa 1
Resistance Considerations
- While fosfomycin shows in vitro activity against multidrug-resistant pathogens, including ESBL-producing organisms, susceptibility testing is not routinely performed in many clinical laboratories 4, 6
- Acquired resistance to fosfomycin has been observed in some cases, particularly with inappropriate use 7
Administration
- Fosfomycin should never be taken in dry form; always mix granules with water before ingesting 3
- Can be taken with or without food 3
By understanding these caveats, clinicians can appropriately prescribe fosfomycin for uncomplicated UTIs while avoiding potential pitfalls in treatment selection and patient management.